1. Field of the Invention
The present invention relates to an electronic frequency converter for a high-frequency immersion vibrator for the compacting of concrete.
2. Description of the Related Art
In the processing of fresh concrete heaps, in order to achieve adequate solidity and tightness of the concrete it is indispensably necessary to remove structural disturbances and air enclosures that arise during the pouring of the concrete, by compacting the concrete. For this purpose, vibrations in the form of high-frequency oscillations are introduced into the fresh concrete heaps, using vibration devices. The vibration devices most often used for this purpose at construction sites are what are known as poker vibrators or immersion vibrators.
Besides the introduction of a particular energy, the form and the frequency of the introduced vibrations are centrally important for an effective compacting of the concrete. In most cases of application, an operating frequency of 200 Hz has turned out to be optimal for the use of immersion vibrators. In order to provide such high-frequency oscillations, immersion vibrators have been widely successful on the market in which a high-frequency electric motor is built into a bottle element that acts as a vibrator housing. These devices are operated via separate mechanical or electronic frequency and voltage converters. However, due to the converters, which are provided separately from the immersion vibrators and whose weight and size give them only limited portability, the radius of possible use of such immersion vibrators on the construction site is considerably limited.
From DE 92 17 854 U, an immersion vibrator for compacting concrete is known that is operated with a high-frequency electric motor. Here, a frequency converter is combined with an actuating switch of the electric motor to form a miniaturized constructive unit, and is housed in a switch housing. In this way, in contrast to conventional high-frequency immersion vibrators, it is possible to do without additional frequency converters, which considerably simplifies the handling of this immersion vibrator for an operator. In addition, here the radius of use of the immersion vibrator is improved as a result of the reduced dimensions of the switch housing and a reduction in weight connected therewith. However, the dimensions of the switch housing cannot be adapted completely to electronic frequency converters having ever-smaller constructions, because an adequate dissipation of heat that is generated during the operation of the frequency converter must be ensured by means of convection via the surface of the switch housing. A further miniaturization of the switch housing would have the disadvantageous consequence that an adequate heat dissipation to the environment would not be ensured, and the frequency converter could thus fail as the result of thermal overloading.